This investigation is concerned with the mechanisms that control blood flow in the cochlea, the degree or magnitude of such control, and the physical locations and effectors of the control. The nature of the blood-perilymph and blood-endolymph barriers are of additional interest as is the influence of the sympathetic nervous system on the cochlear blood supply. In-vivo blood flow velocity and blood vessel diameters are to be measured using light microscopic techniques. Analog and digital techniques will allow quantification of flow and vessel diameter changes for altered systemic blood pressure, cervical sympathetic ganglion electric stimulation, CO2 and O2 exposure, osmotic agents, and intense sound. Extensive use will be made of fluorescence microscopy using flurescein-isothiocyanate-labeled dextran and fluroescently labeled red blood cells. The dyes will be excited by xenon light epl-illumination or transillumination and recorded by an image intensified video camera and recording system. Quantitative analysis of cochlear vasculature will be accomplished by digital image processing techniques. Laser Doppler flowmetery will be used to determine cochlear blood flux changes and studies will be carried out to enlarge the understanding of the performance of this instrumentation. Expanded knowledge of laser-Doppler flowmetry will help bring this instrumentation closer to the possible future clinical application for the measurment of inner ear perfusion. Laser- Doppler flowmetry will be examined in experiments deriving comparative analytical measures of functional changes in cochlear blood flow which are assessed by hydrogen clearance (to measure regional blood flow), by oxygen sensitive microelectrodes (to measure intracochlear pO2), and from compound action potential responses (to test inner ear function). Autoregulation in the inner ear will be investigated by physically controlling systemic blood pressure with the aid of an extracorporeal blood recirculation system. The ultimate goal of the research is to determine the factors that influence cochlear microcirculation and the effect that circulation changes have on the inner ear. The studies will help us to understand normal homeostasis of the inner ear and clarify the role that microcirculation has in sudden deafness, fluctuant hearing, sound-induced hearing loss, and Meinere's disease.